Since the demand for portable devices has rapidly increased in recent years, smartphones and tablet PCs now far outnumber personal and notebook computers and quick improvement has also been made in smartphones. For example, being light and small and having largely improved performance, smartphones have higher and higher heating density, so that heat dissipation thereof has become an important issue. Generally, passive heat dissipation devices are widely used in most portable devices in view of the light weight and small volume thereof. Heat produced by electronic elements needs to be transferred to an outer side of a case of the portable device and dissipates into ambient air by way of natural convection and radiation. For the portable device, since the performance of the screen is very likely adversely affected by increased temperature, the heat produced by the electronic elements is normally transferred to a back case of the portable device via an internal heat transfer design without being transferred to the screen.
When the portable device operates, the temperature distribution on the back case of the portable device is uneven, and local hot spots tend to form at positions with electronic elements of high heating density, such as the central processing unit (CPU), the power amplifier (PA), the graphical display unit (GDU), or the battery, to result in rising temperature of the portable device. Apart from the problem of heat dissipation, the rising temperature of the portable device also tends to cause a burn of a user's skin that is in contact with the heated portable device for long hours.
Furthermore, during communication over the smartphone, the rising temperature of the smartphone also causes rising temperature and discomfort around the user's ear. Therefore, it is desirable to work out a way for effectively transferring the heat from the back case of the portable device to the ambient air, so as to prevent the heat from concentrating on the back case of the portable device, eliminate the forming of local hot spots on the back case, and lower the high temperature at local areas.